x + y = 3 ------equation 1
x - y = 1 -----equation 2
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From equation 2
x - y = 1
Transpose -y to the right side of the equation
x = y + 1 -----equation 2'
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Substitute equation 2' to equation 1
x + y = 3
(y+1) + y = 3
y + 1 + y = 3
transpose 1 to the right side
y + y = 3 - 1
2y = 2
y = 1
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Substitute y=1 to equation 2'
x = y + 1
x = 1 + 1
x = 2
